The present invention is directed to cellular communications systems and in particular to ways of controlling such systems' wireless-transmission power.
We hereby incorporate by reference commonly assigned co-pending U.S. patent application Ser. No. 08/146,364 now U.S. Pat. No. 5,535,240 of Carney et al. for a TRANSCEIVER APPARATUS EMPLOYING WIDEBAND FFT CHANNELIZER AND INVERSE FFT COMBINER FOR MULTI-CHANNEL COMMUNICATION NETWORK, which was filed on Oct. 29, 1993, and describes an advantageous arrangement of cellular-telephone-system base-station receiver and transmitter circuitry. That arrangement contributes to hardware savings because it provides a way of sharing different channels' signal processing in common hardware. It generates a digital signal that is a composite of a plurality of frequency-division-multiplexed digital channel signals. Several channels' radio-frequency signals can be generated from that one composite signal by a single conversion to analog form and translation to the radio frequency, and a common power amplifier can amplify the result for transmission. This can yield significant savings.
Savings result not only because a single power amplifier replaces the many amplifiers respectively dedicated to individual channels but also because the total power capacity for a single power amplifier need not be as great as that for many individual-channel power amplifiers. Although given cell design dictates the power that a base station must be able to transmit into all wireless channels, it does not follow that the power of which a common power amplifier must be capable equals the product of that power level and the number of cell channels; it is highly unlikely that all mobile stations in a given cell will be so positioned as to require that the base station transmit maximum power to all of them simultaneously. So if the base station transmits into each channel only the power necessary to reach that channel's mobile unit, one can limit the installed power capacity for a given cell. This can be accomplished by simply having the mobile unit report to the base station the power level that the mobile is receiving, and the base station can then simply adjust the power that it transmits into that channel until the mobile station reports that it is receiving a target power level. Since it is a feature of certain cellular-telephone communications protocols that the mobile station monitors the power level of its received signal and reports that level to the base station as part of the protocol control information, the power that the base station transmits into each channel can readily be optimized when such protocols are employed.
However, not all cellular-communications protocols provide for the mobile station to inform the base station of the received forward-channel power, i.e., the power transmittal from the base station to the mobile unit, as opposed to the reverse-channel power transmitted from the mobile unit to the base station. In the absence of this information, base stations conventionally transmit into all forward channels with maximum power, so installed capacity cannot be reduced.